This invention relates to a sheet feeding apparatus for use in a reproducing machine and to a reproducing machine incorporating such an apparatus.
One of the difficulties which arises in reproducing machines, particularly compact ones is that undesirable interactions take place between the sheet feeder and the mechanism for registering the sheet with respect to an image to be transferred to it. In a compact environment a sheet upon reaching the registration mechanism still may be acted upon by the original sheet feeding means. This problem has arisen, for example, in machines such as the Xerox "3100" and "4000" copiers. In these machines a sheet is fed from the stack against registration device such as a gate to forward buckle it. After buckling against the gate, the lead edge of the sheet is engaged by registration rolls which come in to pinch and the feed rolls are either cammed out of the way as in the 4000 machine or the stack is cammed out of contact with the feed rolls as in the 3100 machine. In this manner the drag effect of the feed roll on the sheet as it is fed by the registration rolls is eliminated. This approach has worked quite satisfactorily and has achieved commercial acceptance. These approaches do, however, require mechanisms for camming the feed roll and the stack out of engagement.
In accordance with this invention the drag of the feeder/separator on the registration rolls can be substantially reduced by the utilization of a pick force for increasing the normal force during feeding. In U.S. Pat. No. 3,048,393, to R. J. Furr et al, a sheet feeder is disclosed wherein sheets are fed from a stack by means of a belt feeder. The belt feeder is pivotally mounted with the pivot point being located outwardly of the plane of the top sheet of the stack. Therefore, when a sheet is being fed a reaction torque is generated about the pivot point which increases the normal force which the feeder exerts against the stack. This increase in normal force due to the frictional resistance of the sheet being fed and the reaction torque generated thereby comprises one form of a pick force in accordance with the prior art. The amount of the pick force generated will vary with the stack height, generally increasing as the stack depletes. This way of generating a pick force is not believed to be the most desirable because of the variability of the pick force with stack height.
In U.S. application Ser. No. 449,307, filed March 8, 1974, now U.S. Pat. No. 3,888,582 and assigned to the assignee of the instant invention, a feed roll arrangement is shown wherein the feed rolls as in the case of the previously discussed patent are suspended below a pivot whereby a pick force is generated during feeding which increases the normal force of the rolls against the sheet to provide proper feeding. In this case, only a single sheet is fed at any given time so that there is no variability in this normal force as a stack depletes.
In U.S. Pat. No. 3,485,489, granted Dec. 23, 1969, a belt feeder and friction retard separator is disclosed. The feed belt is pivoted about the drive shaft between a position wherein it engages the stack and a retard device and a position wherein the nip between the retard device and the belt feeder is separated. If the belt feeder of this patent was able to pivot about the drive shaft during the feeding operation, then a resistance torque would be generated which would provide a pick force due to the frictional resistance of the belt-retard pad nip. However, the feeder is not arranged to pivot during feeding.
In U.S. Pat. No. 3,279,787, granted Oct. 18, 1966, to Niccole, feed rolls are pivotally mounted about the axis of the drive input. In this feeder a pick force would be generated during both the rearward and forward feeding cycles. In the forward cycle the pick force arises due to the drive direction about the pivot.
In U.S. Pat. No. 3,768,803, a friction retard separator of unique design is described. This separator has proved to be a highly reliable means for feeding individual sheets one at a time from a stack. It is disclosed to be useful for both top feeders and bottom feeders. A wide variety of approaches to mounting the separator are described including a pivotal mounting which allows the separator to pivot against the stack as the stack depletes. In the disclosed separator a feed belt is supported for movement about a pair of pulleys. A curved retard means is positioned against a section of the belt between the pulleys to form a sheet queing throat. The belt contacts the stack near the edge and the throat acts to que or align the sheets for advancement into a sheet handling system. In this system only the topmost sheet is fed through the separator. However, adjacent sheets are shingled in the throat formed between the belt and the retard pad.
Another problem which results when a feed means is continuously in contact with the stack during both the feeding and registration cycles is a wrinkling problem caused by the uneven force distribution in the sheet. The registration rolls or other similar advancing device are spaced across the transverse width of the sheet, whereas the feed means is normally centrally located or located virtually at a single point. This results in an uneven force distribution and can cause wrinkling of the lead edge of the sheet and consequent deletions in the image transferred to the sheet. In accordance with one embodiment to the present invention this problem is overcome by utilizing registration rolls wherein the outer most rolls on each side are toed-out with respect to the feed direction to direct the side edges of the sheet outwardly.
In the previously noted U.S. Pat. No. 3,485,489, the use of a singled toed-out roll for guiding a sheet into contact with a suitable guide surface is described. This reference discloses the use of a toed-out roll for moving a sheet in a sideways direction in addition to the movement in the feeding direction. The toed-out roll is not utilized for taking wrinkles out of the sheet or for otherwise smoothing out the lead edge of the sheet.
In U.S. Pat. No. 2,289,502, toed-out rolls are utilized on either side of a sheet feeder in order to provide corner buckling. Here again, however, there is no suggestion of utilizing toed-out rolls for smoothing out the lead edge of a sheet for imaging.
In U.S. Pat. No. 3,430,952, to Benjamin, a sheet transport belt with herringbone-like projections is utilized to provide simultaneously, opposite, transverse stroking effects to smooth out wrinkles in a sheet.
Yet another aspect of an embodiment of the present invention involves the utilization of a retard pad conforming baffle or paper chute arrangement which causes the entire transverse width of the sheet to traverse the same finitely curved path as the portion of the sheet which is engaged by the nip of a fraction retard separator. By supporting the entire width of the sheet so that it passes through the same curved path wrinkling of the sheet which can result due to the one portion of the sheet passing through a curved path and the remaining portion trying to go in a straight path is reduced. The previously noted U.S. Pat. No. 3,485,489, provides a comparatively straight nip in the friction retard separator, and includes a support plate which supports the transverse width of the sheet while it is in the nip of the separator, however, the support plate is flat.